Exposure devices utilized to manufacture color picture tubes

ABSTRACT

IN AN EXPOSURE DEVICE UTILIZED TO MANUFACTURE A COLOR PICTURE TUBE OF THE CLASS COMPRISING A SOURCE OF LIGHT AND A CORRECTION LENS HAVING A DISCONTINUOUS SURFACE CONSISTING OF A PLURALITY OF DIVIDED REGIONS AND PORTIONS INTERCONNECTING ADJACENT DIVIDED REGIONS, WHEREIN THE DIVIDED REGIONS AND THE PORTIONS THEREBETWEEN HAVE DIFFERENT LIGHT TRANSMISSION CHARACTERISTICS AND THE LIGHT EMANATED FROM THE SOURCE OF LIGHT AND TRANSMITTING THROUGH THE CORRECTION LENS IS USED TO ILLUMINATED THE PHOSPHOR PHOTO-RESIST COATED ON THE INNER SURFACE OF THE PANEL OF THE TUBE, THERE IS PROVIDED A FILTER INTEGRAL WITH OR INDEPENDENT OF THE CORRECTION LENS. THE FILTER IS CONSTRUCTED TO HAVE OPPOSITE DISTRIBUTION PATTERN OF THE LIGHT TRANSMISSION CHARACTERISTICS TO THAT OF THE CORRECTION LENS THEREBY PROVIDING A UNIFORM DISTRIBUTION OF THE LIGHT PASSING THROUGH THE FILTER AND THE CORRECTION LENS AND ILLUMINATING THE PHOSPHOR.   D R A W I N G

y 7 4 EllCHl YAMAZAKI ErAL 3,809,558

EXPOSURE DEVICES UTILIZED TO MANUFACTURE COLOR PICTURE TUBES Filed March 2, 1972 2 sheets-sheet 1 PRIURART 1 TAL May 7, 1974 EHCHI YAMAZAKI E 3,809,558

EXPOSURE DEVICES UTILIZED TO MANUFACTURE COLOR PICTURE TUBES Filed March 2, 1972 2 Sheets-Sheet 2 A IZIZJIZHZIMMIQMIQHZIZIZJWHIQ ZZZZEEQEEEZZZEE ZZEQQQQEZZZQEE BENEENNNNNEIEI E mm 128 Z2 @Z 2% EM] BE mm WW1 SESSSEESESS QQSQSSSESE United States Patent Office 3,809,558 Patented May 7, 1974 US. Cl. sis-45.1 4 Claims ABSTRACT OF THE DISCLOSURE In an exposure device utilized to manufacture a color picture tube of the class comprising a source of light and a correction lens having a discontinuous surface consisting of a plurality of divided regions and portions interconnecting adjacent divided regions, wherein the divided regions and the portions therebetween have different light transmission characteristics and the light emanated from the source of light and transmitting through the correction lens is used to illuminate the phosphor photo-resist coated on the inner surface of the panel of the tube, there is provided a filter integral with or independent of the correction lens. The filter is constructed to have opposite distribution pattern of the light transmission characteristics to that of the correction lens thereby providing a uniform distribution of the light passing through the filter and. the correction lens and illuminating the phosphor.

BACKGROUND OF THE INVENTION This invention relates to an exposure device utilized to manufacture color picture tubes and more particularly to improvements of a correction lens system.

As is well known in the art the fluorescent screen of a shadow mask type picture tube is formed by regularly applying a plurality of trios of phosphors of three'colors onto the inner surface of the panel of the tube by photographic technique. The exposure necessary to form the fluorescent screen is performed by using an exposure device including a source of light and a correction lens system. Since the correction lens is utilized for the purpose of causing the locus of the exposure light beam to approximate the locus of the electron beam, the surface of the correction lens is shaped to have an extremely complicated curved surface. v

The surface of the conventional correction lens generally takes the form of a continuously curved surface. With a correction lens having such a continuously curved surface it is impossible to cause the locus of the exposure light to perfectly or nearly perfectly approximate with the locus of the electron beam so that it has been impossible to perfectly approximate the phosphor dots with the electron beam spots over the entire surface of the panel. For this reason, in a color picture tube having a fluorescent screen formed by using a correction lens having such a continuously curved surface it has been inevitable to accompany the problem of color shading, thus impairing the quality of the reproduced picture.

FIG. 1 of the accompanying drawings shows a plane view of an improved correction lens which has been proposed, FIG. 2 shows a cross-section thereof and FIG. 3 shows a plane view of a panel formed by utilizing this lens. More particularly, as shown in FIGS. 1 and 2 the effective surface of lens 1 is divided into a plurality of regions 2 each being finished to have a flat or curved surface. In the illustrated example, adjacent regions are inclined in the same direction and are interconnected by steep edges 3. With this correction lens, although it is possible to cause the locus of the exposure light to substantially coincide with the locus of the actual electron beam prevailing in the color picture tube, since the light transmission characteristic of the steep edges 3 between adjacent regions is different from that of the individual regions 2 there is formed a grid shaped exposure shading or unevenness on the fluorescent screen formed on the inner surface of the panel corresponding to the sharp edges, as diagrammatically shown in FIG. 3. Accordingly, this grid shaped exposure shading of the fluorescent screen is seen from outside of the tube whether the tube is operating or not, thus impairing the quality of the picture.

SUMMARY OF THE INVENTION It is an object of this invention to provide an improved exposure device utilized to manufacture color picture tubes which can assure substantially uniform distribution of the exposure light upon the phosphor photo-resist on the inner surface of the panel of the tube thereby eliminating the uneven exposure described above.

According to this invention, there is provided a color picture tube of the class comprising a source of light and a correction lens having a discontinuous surface consisting of a plurality of divided regions and portions interconnecting adjacent divided regions, wherein the divided regions and the portions therebetween have different light transmission characteristics and the light emanated from the source of light and transmitting through the correction lens is used to illuminate the phosphor photo-resist coated on the inner surface of the panel of the tube so as to form a fluorescent screen, characterized in that a filter independent of or integral with the correction lens is combined with the correction lens and that the filter has an opposite distribution pattern of the light transmission characteristic to that of the correction lens thereby providing a uniform distribution of the light passing through the filter and correction lens and illuminating the phosphor.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:

FIG. 1 shows a plan view of a prior art correction lens having a discontinuous surface;

FIG. 2 shows a sectional view of the correction lens shown in FIG. 1 taken along a line II-II;

FIG. 3 is a plan view of the panel of a color receiving tube having a fluorescent screen formed by utilizing the correction lens shown in FIGS. 1 and 2;

FIG. 4 shows a sectional view of one example of the exposure device embodying the invention and FIG. 5 is a plan view showing the filter utilized in the exposuredevice shown in FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIGS. 4 and 5, the exposure device 5 embodying the invention comprises a source of light 6, a correction lens 7 for causing the locus of the light beam emanating from the source 6 to approximate the locus of the electron beam actually used in the tube, and a filter 8 combined with correction lens 7. A panel 10 equipped with a shadow mask 9 of the color picture tube is mounted on the upper end of the exposure device. Accordingly, the inner surface of the panel 10 is exposed to the light beam emanated from the source of light and transmitting through correction lens 7, filter 8 and the perforations of the shadow mask 9. Correction lens 7 has the same construction as that shown in FIGS. 1 and 2. In other words, the effective surface of the lens is divided into a plurality of inclined regions which are interconnected by steep edges having a light transmission characteristic different from that of the divided 3 regions. Thus, the surface of the correction lens is discontinuous. According to this invention, filter 8 is constructed to have a light transmission characteristic opposite to that of the correction lens. More particularly, as shown in FIG. 5, the regions 11 of the filter 8 corresponding to regions 2 of the correction lens 7 have the same light transmission characteristic as the sharp edges 3, that is the portions interconnecting the divided regions 2, whereas the regions 12 between regions 11 of the filter 8 which correspond to sharp edg s 3 of the correction lens have the same light transmission characteristic as the regions 2 of the correction lens. Consequently, filter 8 forms a light pattern of a contrast opposite to that of the grid shaped light pattern formed on the inner surface of the panel and is shown in FIG. 3. Such a filter can be readily prepared by exposing a photographic plate through the correction lens. 'In this manner, in the novel exposure device, since the distribution patterns of the light transmission characteristics of the correction lens 7 and the filter 8 are opposite with respect to each other the light transmission characteristic of the combination of the correction lens and the filter becomes substantially uniform thus assuring uniform illumination of the entire inner surface of the panel. Thus, the fluorescent screen of the color receiving tube manufactured by using the novel exposure device has uniform appearance thereby producing pictures of excellent quality.

It should be understood that the filter 8 may be positioned on the side of the correction lens 7 which is the same or opposite to the source of light 6. Instead of forming the filter on a photographic plate, the filter can also be formed by applying a semitransparent substance onto portions 11 of a glass plate at portions corresponding to regions 11 of correction lens 7. Alternatively, instead of providing a separate filter, and a semitransparent substance may be applied directly onto the divided regions of the correction lens 7 to form an integral filter.

As above described, the invention provides a novel exposure device capable of uniformly illuminating the phosphor on the inner surface of the panel of a color picture tube thereby assuring excellent quality of the reproduced picture.

What is claimed is:

1. In the method of forming a color image screen for a cathode ray tube including the steps of directing light from a source of light through correction lens having discontinuous surfaces consisting of a plurality of divided regions and edge portions interconnecting adjacent divided regions, said divided regions and the portions therebetween having different light transmission characteristics, the light emanating from said source of light and transmitted through said correction lens being used to illuminate the phosphor photo-resist coated on the inner surface of the panel of said tube so as to form the desired latent image on said screen, the improvement comprising the step of forming the surface of said correction lens to have an approximately opposite distribution pattern of the light transmission characteristic to that of said correction lens itself thereby cancelling the stripe shaped exposure shading caused by the discontinouous correction lens and providing a uniform distribution of light passing through said filter and said correction lens.

2. In the method of forming a color image screen for a cathode ray tube including the steps of exposing a phosphor and photo-resist coating on the face plate of said tube from a source of light through a correction lens system, the light emanating from said source of light and transmitted through said correction lens system being used to illuminate said photo-resist so as to form the desired latent image on said photo-resist for forming said screen, the improvement which comprises imaging said light source on said photo-resist through a correction lens having discontinuous surfaces consisting of a plurality of divided regions and edge portions interconnecting adjacent divided regions, said divided regions and the portions therebetween having different light transmission characteristics, with said divided regions refracting said light onto said photo-resist over the area of said face plate substantially to coincide with the locus the electron beam will have in said tube and said edge portions diffusing said light at the boundary of saidregions, said light also being transmitted during the same exposure through a filter in registry with and having a distribution pattern approximately opposite that of the light transmission characteristics of said correction lens thereby cancelling the stripe shaped exposure shading caused by said edge portions and providing a uniform distribution of the light passing through said filter and said correction lens to illuminate said photo-resist.

. 3. Themethod according to claim 2 including the step of transmitting said light through said filter in the form of a semitransparent substance onto a transparent plate.

4. The method according to claim 2 including the step of transmitting said light through said filter in the form of a semitransparent substance directly on said regions of said correction lens.

References Cited UNITED STATES PATENTS 3,211,067 10/1965 Kaplan -1 3,259,038 7/1966 Burdick 95-1 3,592,112 7/1971 Frey 951 3,385,184 5/1968 Ramberg 951 JOHN M. HORAN, Primary Examiner 

